This disclosure relates to electronic communication. More particularly, the disclosure relates to electronic communication of the type that employs what is known as persistent scheduling.
Certain types of electronic communication can make use of any one of two or more (i.e., a plurality of) different modulation and coding schemes (“MCSs”) for communication at different times, depending on the condition of the communication or transmission link at such different times. Examples of different types of modulation that may be used are quadrature phase shift keying (“QPSK”), 16-quadrature amplitude modulation (“16-QAM”), 64-quadrature amplitude modulation (“64-QAM”), etc. Examples of different types of coding that may be used are tail-biting convolutional codes (“TBCC”) or convolutional turbo codes (“CTC”) with various specific code rates of 1/4, 1/2, 3/4, and the like. Thus MCS in this disclosure means the combination of modulation and coding rate, such as QPSK 1/4, QPSK 1/2, 16-QAM 1/2, 64-QAM 1/2, 64-QAM 3/4, and the like. The different MCSs provide trade-offs between bandwidth efficiency and transmission reliability. For example, one such MCS may have greater transmission reliability than a second such MCS. The first MCS may therefore need to be used to achieve satisfactory communication while the condition of the transmission link is relatively poor. However, such a greater-reliability MCS may be relatively slow and/or may consume greater bandwidth. Therefore, when communication link conditions improve, it may be advantageous to switch to use of another MCS with lesser but still adequate transmission reliability.
The type of communication known as persistent scheduling employs one burst of initiation command signals followed by a specified number of successive bursts of “payload” data signals. Among other parameters, the initiation command burst establishes what MCS will be used for all subsequent payload bursts (at least until the next full initiation command burst). Persistent scheduling can be efficient because persistent scheduling confines all set-up instructions to the initiation burst, and then allows several payload bursts to be transmitted free of such set-up information. This makes the payload bursts more efficient. A problem or inefficiency can arise, however, if transmission link conditions change significantly subsequent to transmission of an initiation burst and during transmission of the following payload bursts. For example, if the transmission link deteriorates, some payload bursts may need to be transmitted more than once until the payload bursts are properly received. On the other hand, if transmission link conditions improve, it is not possible to take advantage of that improvement by switching to a more efficient MCS until after completion of the full persistent scheduling sequence, when another full initiation burst can be sent to change the MCS.